The present invention is directed to an improved process and apparatus for treating fluids having solid particles suspended therein, and particularly such an improved process or apparatus which will result in improved efficiency in yield.
More particularly, the present invention is directed to such a process and apparatus employing a granular ion exchange or adsorbent material to achieve an ion exchange or adsorption treatment of fluid, for example liquid, to be treated.
Even further, the present invention relates to all types of chemical engineering operations and systems employing such granular ion exchange or adsorbent material which is periodically subjected to a regeneration operation between normal treatment operations during which the fluid is treated. Such systems or operations are conventionally carried out, for example, in sugar refining, in hydrometallurgy, in the treatment of industrial wastewater, and particularly for demineralization of water by ion exchange resins. Accordingly, the following discussion will refer to the present invention as relating to an ion exchange resin system. It is however to be understood that the present invention is not intended to be limited thereby but rather applies to all such operations and systems within the above-discussed scope.
Various types of ion exchange systems are known wherein a liquid to be treated is percolated downwardly through an ion exchange resin bed, and wherein regeneration and washing of the resin bed is achieved by respective upward liquid flows. This type of countercurrent regeneration suffers from one inherent difficulty. That is, in order to achieve an efficient regeneration, the resin bed must be in a relatively compact state when it is traversed by the liquid regeneration agent. However, the ion exchange resins have a density or specific gravity very close to that of the regenerating agent solution, and thus the resin bed tends to be fluidized under the action of the rising flow of liquid regenerating agent through the bed. This fluidization of the resin bed considerably reduces the efficacy and efficiency of the regeneration of the resin bed as a whole, and particularly the lower portion thereof.
Numerous prior art systems have been developed in an attempt to remedy this known disadvantage. Such prior art systems are intended to prevent or inhibit fluidization of the resin bed during regeneration and to promote a homogeneous distribution of the liquid regenerating agent across the bed of granular material.
These known prior art systems may generally be divided into three categories.
A first category of such known systems involve the so-called "water blocking" processes, wherein, for example as disclosed in U.S. Pat. No. 2,891,007, a return collector for the liquid regenerating agent is disposed below the surface of the resin bed. During regeneration, there is a liquid flow in a downward direction which is collected and removed by the collector. Thus, a liquid pressure is achieved over the resin bed. In practice however, it has been found that the resin bed does not remain sufficiently compact, and that the regeneration yield is undesirably low. For example, approximately only 60 to 65% of the resin bed is regenerated. Therefore, the quality of the liquid subsequently treated by the thus regenerated resin bed is undesirably low.
A second category of known systems involve processes of the "air blocking" type, such as disclosed for example in U.S. Pat. Nos. 2,855,364 and 3,687,843. According to this system, a compressed gas is introduced into the top part of the container housing the resin bed, and such gas leaves through a regenerating liquid emptying collector which is disposed approximately ten to thirty centimeters below the upper surface of the resin bed. The operation of this system is conducted in such a manner as to maintain pressure within the interior of the container during the regeneration operation. In a modification of this type of system, there is disclosed in French Pat. No. 72 24 135, a system whereby the top layer of the resin is dried by suction resulting from asperation by a hydroejector. A cover is employed to oppose the expansion of the lower layers of the resin bed. In all of these systems, the container housing of the resin bed is furnished at the level of the resin surface with a grid or with a collector having plungers, whereby the regenerating solution, after having passed through the resin, bed is recovered at the level of the apertures of the collector or of plungers, simultaneously with a variable amount of air. This type of system enables a regeneration yield as high as 75%, but is accompanied by the disadvantage of requiring complex and therefore costly equipment.
A third category of known systems are referred to as "mechanical blocking" systems, whereby there is installed above the resin bed a device which is to reliably maintain a compact state of the resin bed. Movable members, membranes, inflatable compression bodies, or a layer of auxiliary material such as described in French Pat. No. 2,022,828, have been employed for this purpose. This type of system is accompanied by the inherent inconvenience of the necessity of employing accessories which are often complex and fragile. Furthermore, cleaning of the resin bed and removal therefrom of accumulated fine particles of resin are difficult to accomplish.
All of the above known systems inherently suffer from at least one of the disadvantages of not sufficiently compacting the bed of granular material, or of requiring complex equipment, with the result that a uniform distribution of the liquid streams in the resin bed during regeneration is difficult to accomplish.
Furthermore, since it is almost always necessary to periodically eliminate from the resin bed suspended material which is removed from the fluid to be treated and retained within the resin bed, these known systems involve arrangements for unpacking and washing of the resin bed. As employed herein the term "unpacking" is intended to refer to a loosening of the resin bed to facilitate removal therefrom of suspended solid particles. Such unpacking is possible in the prior art systems due to the fact that the resin bed specifically does not totally fill the treatment container, but rather normally fills only approximately 50% to 60% thereof. However, unpacking and washing as carried out in the known systems, normally by injecting water into the resin bed at the base thereof, is less efficient than would be desired, since the speed of the injected water cannot exceed the entrainment speed of the particles to be removed. Furthermore, simple washing of the resin bed by injection of water is likely to be insufficient.